DESCRIPTION(Adapted from applicant's abstract): The synapse is the elemental unit of information processing and storage in the nervous system. Modulation of synaptic strength is widely believed to be the mechanism by which information is encoded in the brain. To understand synaptic plasticity, the specialized form of vesicle secretion that underlies neurotransmission must first be understood. The present studies use an experimental preparation of an isolated lamprey spinal cord in vitro. This preparation allows unparalleled access to a single pre-synaptic element for microinjection and the ability to record from neurons which receive monosynaptic inputs from such an element. Upon injection of various active compounds, the effects of these injections can be monitored as changes in the secretion of neurotransmitter and by alterations in synapse ultrastructure. Preliminary results indicate that synaptic vesicle endocytosis appears to be highly dependent on F-actin and that F-actin may serve as a scaffold by which synaptic vesicles return to the vesicle cluster following endocytosis. The studies proposed will involve injecting a variety of actin modifying agents directly into the pre-synaptic element of a living synapse and measuring the effects such injections have on neurotransmitter release and synaptic ultrastructure. The type of morphological alterations that occur in response to these injections will enable estimation of where in the synaptic vesicle cycle the reagent is having an effect. F-actin binding, disrupting, and capping agents will be injected. In addition, experiments will seek to determine if a major actin binding protein family (myosins), recently localized to nerve terminals, have actions in vesicle exocytosis or endocytosis. These studies will involve cloning lamprey homologues of myosin II and V, production of specific antibodies that disrupt myosin/actin interactions and injections of these antibodies into pre-synaptic regions. The effect such injections have in synapse ultrastructure and physiology will be assessed.